A set of XSLTs to transform NOAA's DWML time-series, 24-hourly, 12-hourly, and glance XML forecasts into JSON.
###Background###
NOAA provides DWML (Digital Weather Markup Language) forecasts in XML format, but they don't offer JSON feeds. I feel like I've written the same XML parsing routines in a number of languages, so I decided to bite the bullet and write it once-and-for-all in XSLT.
Note: This XSLT is written to the 1.0 specification to be compatible with as many XSLT libraries as possible.
I also cleaned up the time-layout mapping nonsense that you have to do when parsing the feeds by hand; each data point has the start time and duration in hours in it. This results in a much larger and more verbose output JSON, but you shouldn't have to manually map time-layout values to arrays.
###Source Feeds###
NOAA provides four main feeds: time-series, 24-hourly, 12-hourly, and glance. There are parameters you can specify to filter the feeds, but in order to make this usable to lots of people, I wrote the transformations against the default values.
Example time-series feed: http://graphical.weather.gov/xml/sample_products/browser_interface/ndfdXMLclient.php?whichClient=NDFDgen&lat=39.7&lon=-104.75&product=time-series
Example glance feed: http://graphical.weather.gov/xml/sample_products/browser_interface/ndfdXMLclient.php?whichClient=NDFDgen&lat=39.7&lon=-104.75&product=glance
Example 24-hourly feed: http://graphical.weather.gov/xml/sample_products/browser_interface/ndfdBrowserClientByDay.php?lat=39.7&lon=-104.75&format=24+hourly
Example 12-hourly feed: http://graphical.weather.gov/xml/sample_products/browser_interface/ndfdBrowserClientByDay.php?lat=39.7&lon=-104.75&format=12+hourly
Consult the NOAA REST API documentation for specific information on the feeds.
###Usage###
You'll probably have to look up the best way to use XSLT in your language/platform of choice, but on OSX and Linux you can use xsltproc:
$ xsltproc noaa.xsl source_file.xml
You can also curl the forecast and pipe it into xsltproc:
$ curl -s "http://graphical.weather.gov/xml/sample_products/browser_interface/ndfdXMLclient.php?whichClient=NDFDgen&lat=39.7&lon=-104.75&product=time-series" | xsltproc noaa.xsl -
Note that you use a dash "-" to tell xsltproc to use stdin.
###Example Output###
You can run the fetch_examples.sh script to generate JSON files for all four feeds. Example files are included in the examples directory.
###Tests###
I don't know of any way to unit test XSLT other than to try feeds with it. NOAA provides feed specifications, so I put those into the test.sh shell script.
I expect there could be edge cases in the feeds that aren't handled properly; send those to me and I'll start a test suite of "bad" feeds.
###Limitations###
XSLT is lousy at pretty-printing, so the JSON it outputs is ugly. (but valid) I like the amazing JQ tool to pretty-print the output:
$ xsltproc noaa.xsl source_file.xml | jq '.'
You can also use the python -mjson.tool command to format the JSON (I think JQ is a faster, but the Python command should be available on your system by default):
$ xsltproc noaa.xsl source_file.xml | python -mjson.tool
You can combine the commands into a one-liner to get pretty-printed output:
$ curl -s "http://graphical.weather.gov/xml/sample_products/browser_interface/ndfdXMLclient.php?whichClient=NDFDgen&lat=39.7&lon=-104.75&product=time-series" | xsltproc noaa.xsl - | python -mjson.tool > sample_time_series.json
These one-line commands are found in the fetch_examples.sh shell script.
###Feedback###
I welcome feedback, pull requests, and bug reports.
If you find a feed that breaks the XSLT, please send it to me in XML format so I can fix the XSLT.